Gas turbines generally operate by combusting a fuel and air mixture in one or more combustors to create a high-energy combustion gas that passes through a turbine, thereby causing a turbine rotor shaft to rotate. The rotational energy of the rotor shaft may be converted to electrical energy via a generator coupled to the rotor shaft. Each combustor generally includes fuel nozzles that provide for delivery of the fuel and air upstream of a combustion chamber, using premixing of the fuel and air as a means to keep nitrogen oxide (NOx) emissions low.
Gaseous fuels, such as natural gas, often are employed as a combustible fluid in gas turbine engines used to generate electricity. In some instances, it may be desirable for the combustion system to be able to combust liquid fuels, such as distillate oil. A configuration with both gas and liquid fuel capability is called a “dual-fuel” combustion system. Certain dual-fuel type combustion systems operate using multiple dual-fuel primary or outer fuel nozzles annularly arranged around a center fuel nozzle. The outer dual-fuel fuel nozzles include breach loaded liquid fuel injection cartridges that provide liquid fuel which may be used to start the engine, increase load, and bring it up to full operating speed. The liquid fuel is ejected in a predominantly axial direction from the end of the fuel nozzle into the combustion chamber.
This type of system typically utilizes water to reduce temperature and emissions to meet the regulations of the region in which the gas turbine is operating. However, water injection via the outer dual-fuel fuel nozzles may result in undesirable thermal gradients that may adversely affect combustor hardware durability.